The present invention refers to an automatic safety syringe.
As is known, a syringe generally comprises a cylindrical body open at the rear to accommodate a plunger. An internally hollow needle is mounted at a head end of the syringe body. By retracting the plunger the liquid contained in a vial is drawn into the syringe body through the needle. By pressing on the plunger the liquid contained inside the syringe body is injected, through the needle, into the patient""s body.
To comply with safety regulations and to avoid the transmission of infections diseases, syringes must generally be used just once and then discarded. For this reason there is a growing demand on the market for disposable syringes able to prevent further use thereof.
Moreover, syringes generally have drawbacks from a safety viewpoint. In fact, once the syringe has been used, the needle remains exposed at the head of the syringe body, with the risk of accidental injuries or needle sticks.
This drawback is overcome in part by European patent EP 0636381 which discloses a protective device for syringe needles. In this case, when the syringe plunger reaches the end of its stroke, the fore end of the plunger shaft catches the needle. When the injection is completed the user must manually retract the shaft; in this manner the needle is pulled by the head of the shaft inside the syringe body into a safety position which avoids accidental needle sticks.
Said solution has problems during hooking of the needle carrier and has the drawback that the user, having completed the injection, can forget to carry out retraction of the shaft, leaving the needle exposed and thus rendering the protective device ineffective.
Patent application PCT WO 99/37345 discloses a disposable safety syringe which provides a needle-covering sleeve axially mounted on the syringe body and slidable from a retracted position, in which it leaves the needle exposed to allow injection, to an advanced position in which it completely covers the needle, preventing re-use of the syringe and acting as a protection against accidental needle sticks.
Once the injection has been carried out the sleeve is automatically brought into the advanced safety position, by means of an automatic mechanism and without any intervention by the user. However, said solution presents a certain complexity for provision and movement of an additional element such as the needle-covering sleeve.
An object of the present invention is to eliminate the prior art drawbacks, providing an automatic safety syringe that is practical, versatile, cheap and simple to make.
Another object of the present invention is to provide such an automatic disposable safety syringe that is able to prevent further attempts at use.
Yet another object of the present invention is to provide such an automatic syringe that is extremely safe and able to prevent accidental injuries and tampering after it has been used.
These objects are achieved in accordance with the invention with the characteristics listed in appended independent claim 1.
Advantageous embodiments of the invention are apparent from the dependent claims.
The disposable syringe according to the invention comprises an internally hollow syringe body open at the front and rear, a plunger that can slide inside the syringe body with an injection stroke extending from a retracted syringe-filling position to a forward syringe-emptying position. The plunger is provided at the rear with a shaft or stem that can be operated manually and brought out of the syringe body through the rear end thereof. The syringe comprises an injection needle integral with a needle-carrier that can be engaged by means of a supporting body to the fore end of the syringe body.
The peculiarity of the invention is represented by the provision of an automatic system which intervenes automatically when the plunger reaches the end of the injection stroke. The automatic device is responsible for releasing the needle-carrier from the supporting body in order to push it inside a chamber defined in the shaft, so as to bring the needle integral with the needle carrier into a safety position.
Said automatic system comprises elastic means disposed under compression between the needle carrier and the supporting body, a diaphragm mounted in the head of the shaft to obstruct the inner chamber of the shaft, and engagement means provided in the head of the shaft able to cooperate with reciprocal engagement means provided in the needle carrier to cause disengagement of the needle carrier from the supporting body, when the plunger reaches the end of the injection stroke. In this manner the elastic means, on expanding, cause retraction of the needle carrier. The needle carrier thus abuts against the diaphragm causing disengagement or rupture thereof which allow the needle carrier to enter the shaft body chamber. In this manner the needle integral with the needle carrier is protected inside the chamber of the shaft body in a safety position.
The advantages of the disposable syringe according to the invention are evident. In fact, once the injection has been completed, the automatic system causes automatic, involuntary re-entry of the needle carrier inside the chamber defined inside the body of the shaft, thus placing the needle in a safety position which avoids accidental needle sticks.